Class 12, Chapter 10
Microbes in Human Welfare
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Microbes are present everywhere–in soil, water, air, inside our bodies and that of
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other animals and plants. They are present even at sites where no other life-form
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could possibly exist–sites such as deep inside the geysers (thermal vents) where the
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temperature may be as high as 100⁰C, deep in the soil, under the layers of snow
several metres thick, and.in highly acidic environments.
Microbes in Household Products
A common example is the production of curd from
milk. Micro-organisms such as Lactobacillus and
others commonly called lactic acid bacteria
(LAB) grow in milk and convert it to curd.
Converting milk to curd also improves its
nutritional quality by increasing vitamin B₁₂.
The puffed-up appearance of dough of dosa and
idli is due to the production of CO₂ gas. Similarly
the dough, which is used for making bread, is
fermented using baker’s yeast (Saccharomyces
cerevisiae). ‘Toddy’, a traditional drink of some
parts of southern India is made by fermenting
Viruses: (a) A bacteriophage; (b) sap from palms. Cheese, is one of the oldest food
Adenovirus which causes respiratory items in which microbes were used. Different
infections; (c) Rod-shaped Tobacco varieties of cheese are known by their
Mosaic Virus (TMV). Magnified about characteristic texture, flavour and taste, the
1,00,000–1,50,000X
specificity coming from the microbes used. For
2007
Bacteria: (a) Rod-shaped, magnified example, the large holes in ‘Swiss cheese’ are
Probiotics → live
1500X; (b) Spherical shaped, magnified --- due to production of a large amount of CO₂ by a
1500X; (c) A rodshaped bacterium microbial food
-- bacterium named Propionibacterium sharmanii.
showing flagella, magnified 50,000X The ‘Roquefort cheese’ are ripened by growing a
supplement.
specific fungi on them, which gives them a
particular flavour.
Microbes in Industrial Products
Used for the production of beverages and
antibiotics.
Fermented Beverages
Microbes especially yeasts have been used from time immemorial for the production of S. ellipsoidens - wine yeast
beverages like wine, beer, whisky, brandy or rum. For this purpose the same yeast S. pireformis - ginger
Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast,
is used for fermenting malted cereals and fruit juices, to produce ethanol. Wine and beer/ ale yeast.
beer are produced without distillation whereas whisky, brandy and rum are produced by
distillation of the fermented broth.
Antibiotics
Antibiotics can kill or retard the growth of other (disease-causing) microbes.
The commonly used antibiotic Penicillin. Penicillin was the first antibiotic to be discovered (by Alexander Fleming
who named it Penicillin after the mould Penicillium notatum.) Full potential was established much later by Ernest
Chain and Howard Florey. This antibiotic was extensively used to treat American soldiers wounded in World War II.
Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali
khansi), diphtheria (gal ghotu), pneumonia and leprosy (kusht rog), which used to kill millions all over the globe.
Chemicals, Enzymes and other Bioactive Molecules Most common
in
substrate used
Microbes are also used for commercial and industrial production of certain chemicals es fo r
distilleri
like organic acids, alcohols and enzymes. Examples of acid producers are Aspergillus
production of
niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; asses.
Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (curd) (a ethanol is mol
2011
bacterium) of lactic acid.
Lipases are used in detergent formulations and are helpful in removing oily stains from Modern detergent
the laundry. Bottled juices are clearer as compared to the juices made at home, this is contain enzyme
because they are clarified by the use of pectinases and proteases. Streptokinase preps. of
produced by the bacterium Streptococcus and modified by genetic engineering is used acidophiles.
as a ‘clot buster’ for removing clots from the blood vessels of patients who have
undergone myocardial infarction leading to heart attack. 2008
Cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients fo r o rg a n
(produced by Trichoderma polysporum, a fungi). Statins produced by the yeast Drug used tients is
s p la n t pa
Monascus purpureus have been commercialised as blood-cholesterol lowering agents. It tran from
acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol. obtained
ma.
Tricho r d e
2011
2017
Microbes in Sewage Treatment
Before disposal sewage is treated in sewage treatment plants (STPs) to make it less polluting.
tre atm ent: Treatment of waste water is done by the heterotrophic microbes naturally present in the sewage.
Primary n d ed
of suspe Primary treatment: physical removal of particles. Initially, floating debris is removed by sequential
removal
solids. filtration. Sedimentation removes soil and small pebbles. All solids that settle form the primary sludge,
and the supernatant forms the effluent, which is taken for secondary treatment.
2011
Secondary treatment or Biological treatment: effluent is constantly agitated mechanically and air is
pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria
Biological process done
associated with fungal filaments to form mesh like structures). This significantly reduces the BOD
by heterotrophic (biochemical oxygen demand) of the effluent. The BOD test measures the rate of uptake of oxygen
bacteria. by micro-organisms in a sample of water and thus, indirectly, BOD is a measure of the organic matter
present in the water. The greater the BOD of waste water, more is its polluting potential.
2011
After the reduction of BOD of sewage, the effluent is passed to a settling tank where ‘flocs’ are
Activity
allowed to sediment which is called activated sludge (rich source of aerobic bacteria). The remaining
of anaerobic
major (some is pumped back into the aeration tank to serve as the inoculum) part of the sludge is
bacteria on
pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow
sewage produces
anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce
marsh gas.
a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas
and can be used as source of energy as it is inflammable.
2012
The most abundant prokaryote
Microbes in Production of Biogas helpful to humans in making curd
Certain bacteria, which grow anaerobically on cellulosic material, produce large
amount of methane along with CO2 and H2. These bacteria are collectively called
from milk and in production of
methanogens, and one such common bacterium is Methanobacterium. These bacteria antibiotics is heterotrophic
are commonly found in the anaerobic sludge during sewage treatment. These microbes.
bacteria are also present in the rumen (a part of stomach) of cattle. A lot of
2012
cellulosic material present in the food of cattle is also present in the rumen. In
rumen, these bacteria help in the breakdown of cellulose and play an important role CH₄ :- 50 to 70%
in the nutrition of cattle. The excreta (dung) of cattle, commonly called gobar, is CO₂ :- 30 to 70%
rich in these bacteria. Dung can be used for generation of biogas, commonly called Biogas H₂
gobar gas. Biogas production was developed in India mainly due to the efforts of H₂S 310
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Indian Agricultural Research Institute (IARI) and Khadi and Village Industries
Commission (KVIC).
2008
Microbes as Biocontrol Agents
as cepacia
Pseudomon Biocontrol refers to the use of biological methods for controlling plant diseases and pests.
ol of Biological control of pests and diseases: The Ladybird, and Dragonflies are useful to get
→ biocontr
disease in rid of aphids and mosquitoes, respectively. An example of microbial biocontrol agents that
nematodal can be introduced in order to control butterfly caterpillars is the bacteria Bacillus
plants.
2019
/Odishal thuringiensis (Bt). These are available in sachets as dried spores which are mixed with
A bioche water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these
mical ag
ent to
be a par
t of an are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the
integrate
d pest
larvae get killed. The scientists have introduced B. thuringiensis toxin genes into plants.
managem Such plants are resistant to attack by insect pests. Bt-cotton increases cotton yield.
ent shou
ld be
species-sp
ecific an Trichoderma species are free-living fungi that are very common in the root ecosystems.
inactive d They are effective biocontrol agents of several plant pathogens.
on non-t
arget
organism Baculoviruses (genus- Nucleopolyhedrovirus) are pathogens that attack insects and other
s.
2019
arthropods. These viruses are excellent candidates for species-specific, narrow spectrum
2010
insecticidal applications. They have been shown to have no negative impacts on plants,
,
, 2009
B . thu r in giensis, mammals, birds, fish or even on non-target insects.
Ex:
lo v ir us,
Bacu
a.
trichoderm Microbes as Biofertilisers
2020(2) Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources
B. thurin of biofertilisers are bacteria, fungi and cyanobacteria. The nodules on the roots of
giensis → leguminous plants (such as soybean) formed by the symbiotic association of Rhizobium.
biocontrol Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples
agents of
lepidopter Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
an plant
pests.
2022
, 2017 Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many
members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations
absorbs phosphorus from soil and passes it to the plant. Additional benefits such as
• Frankia → alnus resistance to root-borne pathogens, tolerance to salinity and drought, and an overall
• Rhodospirillum → anaerobic, increase in plant growth and development are also seen.
free living N₂ fixer. Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial
environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc,
• Anabaena → N₂ fixer.
Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue
• Rhizobium → alfalfa. green algae also add organic matter to the soil and increase its fertility.
2013
2010 Endomycorrhiza
Besides paddy fields,
cyanobacteria are also
found inside vegetative
part of cycas.
